The present invention relates to a method of making printed circuit boards (PCBs), and particularly to a method of easily forming the printed circuit patterns on either side of the PCBs, and also relates to the PCBs thereby made.
It is generally known that the PCBs are not only used in electronics, but also in circuits for much other electrical equipment. The development of such electrical equipment is fast and obstacles are found only in the manufacturing process of the PCBs. In fact, the widespread conventional process is long and expensive. It involves a great deal of wasted material, some of which is precious. Additionally, it leads to considerable ecological problems to eliminate the wasted material.
The conventional manufacturing process adopted by almost all PCB manufacturers involves, in its initial portion, at least the following steps:
1. application of a CAD processor output to a photographic plotter, which has the disadvantage of having to operate in a dark room; PA1 2. preparation of a set of films (at least three films, i.e., two for the two faces and one for the solder resist); if six layers are required, six films are necessary plus the solder resist film mask, such films corresponding to the photographic negatives. PA1 3. use of silk screen racks; PA1 4. coating of the photographic emulsion; PA1 5. contact printing in which the films produced in step 2 are positioned one at a time and illuminated to obtain a positive; PA1 6. development; PA1 7. completion of the silk screen (i.e., the circuit layout); PA1 7'. obtaining the finished silk screen with solder resist; PA1 8. operations such as finishing, drilling and blocking-out.
FIG. 1 illustrates a simplified example of a conventional process by showing the shapes that the PCB assumes during preparation; FIG. 1A shows how a layer of copper Cu is applied to each major face I and II of a thick and rigid dielectric support S; FIG. 1B illustrates a layer of plating resist R applied to uncovered sections I and II, whereas area III is not covered by the resist R. In FIG. 1C, a layer of tin-lead (Sn-Pb) is applied to III. In FIG. 1D, all of the masking plating-resist R is taken away whereby the Cu layer covered by Sn-Pb is uncovered only in zone III; and in FIG. 1E chemical etching is carried out which removes the whole initial layer of copper as well as the one in zone III protected by the Sn-Pb layer that does not resist the chemical attack.
Moreover, to produce drilled boards, drilling must be done immediately after the operation of FIG. 1A. However, to internally metallize the holes, layers of chemical copper are first applied and are followed by layers of galvanic copper on both faces I and II. Afterwards, the procedure shown in FIG. 1B is followed, i.e., covering, application of Sn-Pb, removal of the plating resist and chemical etching. As already pointed out, the conventional processes are not only time consuming but are also expensive as regards waste material. This gives rise to pollution when eliminating the waste material.
In particular, the conventional process does not only involve many operations like the above-mentioned preparation of negative (2), silk screen racks (3), layout of photographic emulsion (4), printing (5) and development (6), but is also redundant in that these operations are repeated at least as many times as there are different layers, in addition to preparing the solder resist. From FIGS. 1A and 1B it can be seen that in order to cover only section III it is necessary to cover in the initial phase all major faces of rigid support S first with copper and then with plating resist R. Almost 90 percent of the copper and resist R is removed and essentially wasted, thus giving rise to the ecological waste disposal.